move the mouse over the add filter button and the USB devices will appear in the display box. This box is active. Select the one you want. If this is not obvious, then you can test this by removing the USB In the example above I have also taken Sasquatch's advice and created an empty filter which will assign all USB devices to the guest operating system. This is however disabled.

Start the VM and wait for Windows to do its plug and play magic.

This process was developed using a Windows Vista 32 bit guest and a Windows Vista 64 bit host, and a patched version of Virtual Vox 2.1.3

I have left the "All Devices" filter disabled. It will do all devices and thus some system devices will become visible to the guest such as the fingerprint reader, and whatever Chicony Electronics provide.

Sasquatch is a regular correspondent at virtual box forums and offered his advice in a thread called "USB on Windows host and Windows guest".